Cell & Molecular

A new screening technique identifies molecules that control the cell cycle

Short stretches of RNA molecules known as microRNAs (miRNAs) coordinate gene expression. Although their importance as gene regulators is now accepted, it can be hard to figure out the functions of particular miRNAs. An individual miRNA molecule can interact with multiple gene transcripts, and multiple miRNAs often serve similar functions and so mask each others' effects.

Using a new screening technique, Robert Blelloch and colleagues at the University of California, San Francisco, have identified a collection of miRNAs that allow embryonic stem (ES) cells to divide rapidly1. The team had previously engineered a line of mouse ES cells that cannot process miRNA because they lack a crucial gene called Dgcr8. Unlike normal ES cells, these knockout ES cells do not proliferate rapidly. By introducing commercially available miRNA mimics, however, the researchers were able to get the cells to start dividing more quickly. After screening nearly 300 mouse miRNAs, the researchers found 14 that greatly improved proliferation of the Dgcr8-knockout ES cells but had no effect on wild-type ES cells. The researchers then concentrated their analysis on five of the miRNAs that are also highly expressed in human ES cells.

Part of the body's inherent healing response is to mobilize progenitor cells from the bone marrow to the site of injury. Rather than trying to collect and purify sufficient numbers of progenitor cells from bone marrow and blood donors, many clinicians hope to find better ways to summon the right types of cells from their natural reservoir in the bone marrow. In a recent study published in Cell Stem Cell, Sara Rankin and colleagues at Imperial College London demonstrate how naturally occurring growth factors can call different types of progenitor cells into duty1.